Congential heart disease is currently considered the most frequently occuring major birth defect. Approximately 95% of these congenital heart defects involve the connective tissue components of the heart. Due to a basic lack of understanding of the contributing factors to congenital heart disease, our efforts of investigating methods of prevention have been hindered. In order to address this challenge, one must first establish the normal sequence of events in mammalian heart development using a dynamic model which could be studied noninvasively, which is one of the specific aims of this project using the guinea pig as a model. This will be accomplished by two-dimensional ultrasound imaging of the developing guinea pig fetus on a daily basis from conception until completion of cardiac formation, probably by the fourteenth gestational day. after the major cardiac structures have been formed, ultrasound imaging of the fetal heart will be performed every other day until birth in order to study all aspects of cardiac formation, remodeling, and maturation. All ultrasound images of cardiac development will be identified and verified by sacrificing the imaged fetuses and performing routine light microscopy and scanning electron microscopy on the fetal hearts. Since many cardiac deviations which occur during morphogenesis critically affect the connective tissue component of the extracellular matrix (ECM), integral morphogenetic macromolecules of the ECM, such as fibronectin, collagen, laminin, and glycosaminoglycans, will also be investigated by immunohistochemical techniques (immunofluorescence and immunoelectron microscopy) using specific antibodies to fibronectin, laminin, and type-specific collagens. This seems like the most direct approach in trying to elucidate the specific role of each ECM macromolecule during precisely-imaged cardiogenic events. After the normal sequence of cardiogenesis is established, using this combined approach, future plans involve interfering with cardiac development by physical and chemical means, which should be very useful in contributing to our knowledge of the origin of human cardiac malformations and to our interpretations of human fetal imaging, in both normal and abnormal conditions.